Building a Foundation

Angular Limb and Flexure Deformities in Foals

Stephen E. O'Grady, DVM, MRCVS

Angular limb and flexure deformities are common limb abnormalities seen in foals that require early recognition and treatment. Foals with angular limb deformities have traditionally been referred to as "knock-kneed" or "bow-legged" in the front limbs. Angular limb deformities can also appear in the hind limbs but not as commonly. The pathogenesis of this problem is not clearly understood but suggested etiologies can be classified as either congenital (present at birth) or acquired in the first few weeks of life. The primary lesion is an imbalance of physeal growth; for various reasons, growth proceeds faster on one side of the growth plate than the other does. A valgus deformity is defined as deviation of the limb away from the midline (knock-kneed); a varus deformity is a deviation of the limb toward the midline (bow-legged). The most common location of angular limb deformity is the carpal joint (knee) where valgus deformities are most often seen.

It is apparent that this knock-kneed conformation offers the newborn a more comfortable stance while eating off the ground, but most things are good in moderation and this deformity may exceed acceptable limits. The deviation that exceeds 5-8 degrees becomes a concern. A few days of stall confinement on firm bedding or limited exercise in a small paddock (one hour twice a day) is a rewarding, cost-effective treatment for the early valgus knee foal.

Radiographs (x-rays) should be part of the physical examination in a foal with an angular limb deformity. Occasionally severe abnormalities involving the bones of the knee or at the level of the affected joint will preclude correction of the problem. X-rays will also reveal the degree of deviation, and allow comparison at a later date.

Conservative therapy for the management of most angular limb deformities is successful in the newborn foal. This would include squaring the toe of the hoof, restricting exercise and occasional splinting. Restricted exercise would be either strict stall confinement or brief periods of turnout in a small area with firm footing for a half hour, two to three times daily. This allows the growth plate to be stimulated but prevents stress and compression on the affected side of the growth plate. If the knee can be corrected by applying pressure with one hand on the inside of the knee and counter pressure with the other hand applied to the outside of the fetlock, then a splint made from polyvinylchloride (PVC) pipe fitted from the elbow to the fetlock can be applied for a few hours daily. A full length bandage is applied to the limb, then the PVC pipe is placed on the outside of the limb and secured with a bandage which pulls the affected joint in that direction. This is the most cost effective and many times the most curative treatment available.

Acquired angular limb deformities can be graded from one to four according to the degree of deviation. These can occur anywhere from a few days onward. Grade one and two angular limb deformities involving the knee will again respond to restricted exercise and the use of an extension which is applied to the inside of the foot. The extension on one side and toward the back of the foot will support the overloaded side of the limb, i.e. will move the plane of support toward the midline to allow a more even distribution of weight over the support surface. The extension also promotes centerline breakover. The extension is made from a poly methylmethacrylate (Equilox®) and fiberglass applied directly to the foot and shaped to the desired width to provide the exact amount of correction. It is trimmed like normal hoof as the foot grows or additional applications can be applied as deemed necessary. Again, splints would be optional depending on the movement of the joint.

If grade three and four angular limb deformities do not respond to conservative therapy (limited exercise, lateral extensions, splints, etc.) they would undergo a surgical procedure such as a periosteal elevation (PE). In severe cases, this could be combined with a staple or screws and wires on the opposite side of the joint if necessary. In many cases, however, the surgical procedure is performed too early before conservative therapy is allowed to correct the problem. It has been shown that angular limb deformities involving the knee will respond to surgery up to four months of age with full correction. Recently, we have taken a different approach to the surgery. Instead of periosteal elevation, we have been removing a very small piece of bone (ulna) with very encouraging results. This procedure can be done under local anesthesia and leaves very little scarring.

Various deformities (bow-legged) involving the fetlock are also very common in thoroughbred foals. This deformity can be congenital or acquired. All acquired varus fetlocks occur within the first few weeks of life. A varus fetlock deformity requires early detection and treatment to correct due to early closure of the growth plates of the fetlock. In the early stages, the foal will have an inward arc to the limb in flight when walked and will stand with the feet closer (to the midline) than the fetlocks. Varus foals respond nicely to a lateral extension (Equilox®) applied to the foot at ten days of age and correction is usually completed at a month. If the foal is presented for treatment after thirty days, then it usually becomes a candidate for a periosteal elevation at the fetlock. With both valgus and varus deformities, the earlier corrective measures are instituted, the faster the problem will resolve.

Flexure deformities have been traditionally referred to as "contracted tendons." The primary defect is a shortening of the musculo-tendonous unit rather than a shortening of just the tendon portion, making "flexure deformity" the preferred term. This produces a unit of functional length less than necessary for normal limb alignment and leads to the clinical signs of upright pasterns, prominent coronary bands and boxy feet. If left untreated, it will lead to a condition where the foal is unable to place the heel of his foot on the ground, resulting in a typical clubfoot.

Flexure deformities present at birth are thought to be the result of intrauterine positioning. These usually resolve in the first few days of life with repeated intervals of brief exercise in a small paddock.

Acquired flexure deformities are thought to be associated with poor nutritional management in foals (increased protein, unbalanced minerals, etc.). It is this writer's belief that this syndrome is not part of the developmental orthopedic disease (DOD) but a response to some form of pain. Any discomfort in the foot or lower limb will initiate the flexion withdrawal reflex which causes flexor muscle contraction and altered position of a joint. I have seen this condition on many farms where the feet were trimmed too short and excess sole was removed from the foot, which causes marked toe bruising. The first clinical sign one may see is abnormal wear of the hoof wall at the toe. A closer look may reveal heat in the feet, an increased pulse, pain on hoof testers, a prominent coronary band and an upright pastern angle. This is the time for conservative treatment: restricted exercise to decrease continued trauma, the judicious use of anti-inflammatory drugs to relieve pain, and the administration of oxytetracycline which will cause muscle relaxation, leading to normal foot-pastern alignment.

At the same time, Equilox® can be applied to the anterior hoof wall to form a toe extension and the fiberglass continued over the solar surface to protect that area from further bruising (Fig. 3). This toe extension forms part of the foot and places continuous tension on the muscular structures above the tendon. If this condition is allowed to persist, it will result in irreversible changes in the foot and joint capsule requiring a surgical procedure for correction (check ligament desmotomy).

A good working relationship between veterinarian and farrier are necessary and important. A regular trimming program for foals is essential and cost-effective when conducted as an examination and maintenance exercise. Foals' feet should be kept balanced, with adequate sole depth and maximum horn length to protect the tender, vulnerable white line and developing coffin bone.

Hoof care in the first four months of life is serious business and should never be taken lightly. Discussion and management with regard to feet and limbs during this period will dictate the success of the foal as a sales yearling or mature athlete. A sound foot care program is time consuming whereas assembly-line trimming is easy, but the former is much more beneficial.

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